The goal of this study to find out the efficacy of early rhythm therapy in patients with subclinical atrial fibrillation detected by Cardiac Electronic Implantable Devices.

Early rhythm therapy includes antiarrhythmic drug, cardioversion, and catheter ablation. The general control group receives general management without the above atrial fibrillation rhythm control treatment.

Researchers will compare early rhythm control groups to general control groups to see if early rhythm therapy works to reduce the atrial fibrillation burden by 50% or more, or decrease the incidence of clinical AF documentation.

Participants will:

• Randomly allocated to two groups at a 1:1 ratio.
• Receive the treatment according to their assigned group.
• Visit the clinic once every three months for checkups and tests.

There have been reports that early rhythm control therapy reduces various heart events in patients with atrial fibrillation. The definition of "early" atrial fibrillation defined in this study was defined as a patient within one year of diagnosis. This means clinical atrial fibrillation diagnosed by 12-lead electrocardiogram.

Atrial high rate episode (AHRE) may be found through various Cardiac Electronic Implantable Devices (CIED), which is defined as subclinical atrial fibrillation. There have been many studies on the risk of such subclinical atrial fibrillation causing cerebral infarction, and meta-analysis results show that there is a high risk of thromboembolism if there is an episode of 30 seconds or the sum of duration is more than 24 hours. However, there is no research on the rhythm control therapy for patients with subclinical atrial fibrillation, and this study might be considered as an important factor in determining the truly early atrial fibrillation treatment guideline. Therefore, this study aims to find out the efficacy of early rhythm therapy in patients with subclinical atrial fibrillation detected by Cardiac Electronic Implantable Devices.

This study is a randomized, multicenter, prospective, interventional study to observe the efficacy of early rhythm control treatment compared to general control treatment in patients with subclinical atrial fibrillation. According to the electronic random assignment program, it is divided into two groups (early rhythm control group, general control group) and allocated at a 1:1 ratio. This study is open-label study. Early rhythm control groups get rhythm control treatment for atrial fibrillation based on guidelines. This includes antiarrhythmic drug, cardioversion, and catheter ablation. The general control group receives general management (observation, heart rate control treatment if necessary) without the above atrial fibrillation rhythm control treatment. In both groups, appropriate anticoagulant treatment is given if there is an indication of cerebral infarction prevention associated with atrial fibrillation.

Inclusion Criteria:

• Among patients with Cardiac implantable electronic device (CIED), subjects with atrial high rate episodes found Cardiac implantable electronic devices: implantable loop recorder, pacemaker, implantable cardioverter defibrillator(ICD), cardiac resynchronized therapy(CRT)
• Patients aged 19 or older who have agreed to the study (if voluntary consent is deemed difficult, consent from legal representatives is obtained together)
• If the accumulated period of the atrial high rate episode during the three-month observation period is more than 21 hours
• Patients whose atrial fibrillation has not been confirmed by electrocardiogram or holter monitoring within the past year from the time atrial high rate episode was detected

However, enrollment is possible even if it includes one of the following two cases ⓐ Patients diagnosed and recorded as atrial fibrillation on medical records but not confirmed by electrocardiogram or holter monitoring

ⓑ If there is a record of atrial fibrillation, but Paroxysmal AF less than 30 seconds

Exclusion Criteria:

• Patients deemed inappropriate to participate in the study by the investigator
• Patients diagnosed with atrial fibrillation with 12-lead electrocardiogram or holter within the past year prior to participation in the study
• Patients taking Class Ic, III of antiarrhythmic drugs prior to study participation
• Patients who have had rhythm control treatments such as Radiofequency catheter ablation (RFCA), Total thoracoscopic ablation (TTA), Maze procedure (MAZEop), and antiarrhythmic treatment due to atrial fibrillation (except for CTI ablation with AFL)
• Patients whose life expectancy is less than one year (e.g., patients who can't even have a heart transplant, patients who receive DNR, Patients in hospice wards who refuse life-sustaining treatment, terminal cancer patients who cannot receive radiation or chemotherapy, etc.)